A wide range of devastating brain injuries cause brain swelling or bleeding. Because the skull is fixed in volume, increases in the volume of its contents result in increases in intracranial pressure (ICP). Elevations of ICP can lead to worsening brain injury or death by compressing either blood vessels supplying the brain or vital brain structures themselves. Detecting and treating such increases in ICP is crucial to protecting the injured brain. Currently, the only methods to monitor ICP are invasive and require direct entry of a probe system through the skull. The major hypothesis of this proposal is that it is possible to monitor changes in intracranial pressure by non-invasive means using acoustic measurements. This method of measurement has significant advantages over current invasive measurements of monitoring ICP in that the measurements can be obtained conveniently and rapidly (in less than a minute) without invading the skull and with zero probability of infection. It is proposed to develop a practical instrument for monitoring changes in ICP using measurements of distortion product otoacoustic emissions (DPOAE) and middle ear impedance. Initial evaluation and refinement of the instrument will involve healthy normal hearing subjects on a tilt table. Subsequent evaluations will compare the instrument with the conventional invasive method of monitoring ICP with patients in the neurological intensive care unit of a major hospital. A wide range of devastating brain injuries cause brain swelling or bleeding. Because the skull is fixed in volume, increases in the volume of its contents result in increases in intracranial pressure (ICP). Elevations of ICP can lead to worsening brain injury or death by compressing either blood vessels supplying the brain or vital brain structures themselves. Detecting and treating such increases in ICP is crucial to protecting the injured brain. Currently, the only methods to monitor ICP are invasive and require direct entry of a probe system through the skull. The major hypothesis of this proposal is that it is possible to monitor changes in intracranial pressure by non-invasive means using acoustic measurements. This method of measurement has significant advantages over current invasive measurements of monitoring ICP in that the measurements can be obtained conveniently and rapidly (in less than a minute) without invading the skull and with zero probability of infection. [unreadable] [unreadable] [unreadable]